Some vehicles may include engines that are configured to vary operation between two or more operating modes. In one example, an engine may be configured to operate in a spark ignition (SI) mode during some conditions and a homogeneous charge compression ignition (HCCI) mode (e.g. which uses controlled autoignition or CAI) under other conditions. By varying operation between SI mode and HCCI mode, efficiency gains may be achieved and emissions may be reduced, while still meeting desired engine output demands.
Engine modes may be selected based on engine operating conditions. For example, as the engine speed or torque is increased to a specific threshold, the engine may be transitioned from HCCI to SI mode so that driver torque demands are met. In another example, when the engine load is within a particular range, the engine may be transitioned from SI to HCCI mode so that fuel efficiency may be increased.
As excessive mode switching may be an issue, one approach to reduce mode switching in an engine with multiple modes is described in U.S. Pat. No. 6,026,781. In the '781 patent, transitions between stratified and premixed spark-initiated combustion may be based on geographical information provided by a navigation system. In this way, certain transitions may be avoided. Further, this approach discloses transitioning from stratified to premixed spark-initiated combustion when the vehicle sharply accelerates and the torque becomes insufficient.
The inventors herein have recognized several issues that may occur in trying to apply the approach of '781 to an HCCI/SI engine. Specifically, because engine torque increases and/or decreases may be achieved more rapidly in SI operation than HCCI operation, the above modifications to mode transitions thresholds may result in the inability of the vehicle to respond rapidly to a driver's request. Further, because mode transitions into/out of HCCI operation may be slower than SI operation, relying on a mode transition when rapid acceleration is requested may be insufficient in some circumstances.
In one example, the disadvantages described above may be addressed by an engine system for a vehicle, comprising: at least one cylinder configured to vary operation between a spark ignition mode and a homogeneous charge compression ignition mode; a navigation system configured to receive navigation information; and a control system for varying operation of the engine between the spark ignition mode and the homogeneous charge compression ignition mode responsive at least to said navigation information, where said information is used by the control system to affect transitions into HCCI mode differently than transitions out of HCCI mode.
In this way, it may be possible to take into account navigation system information in selecting whether to transition operating modes, and further it may be possible to adjust mode transitions differently responsive to the navigation system information. Thus, the navigation information, along with the different performance capabilities between SI and HCCI combustion, may be used to provide improved mode selection and appropriate transitions. In one particular example, the control system may utilize different navigation criteria for transitions out of SI operation (or into HCCI operation) than transitions into SI operation (e.g., out of HCCI operation).
Further, in one example, the control system may vary said operation between the spark ignition mode and the homogeneous charge compression ignition mode responsive to a driving pattern of a vehicle operator driving the vehicle.
In this manner, future engine operating conditions may be predicted by navigation information and/or human/machine interface (HMI) measurements, thereby providing sufficient opportunity to transition between SI and HCCI modes. Further, transitions may be reduced, in some conditions, by reducing some transitions to modes that are predicted to be brief in duration or unsuitable for the predicted future operating conditions or the driving pattern of the vehicle operator.